JP4985446B2 - EGR control device for internal combustion engine - Google Patents

Description

  The present invention relates to an EGR control device for an internal combustion engine.

  As a technique for reducing exhaust emission and improving fuel efficiency of an internal combustion engine, an EGR device that returns part of the exhaust from the internal combustion engine to the intake system as EGR gas is known.

  In addition, there is known a technique for improving fuel efficiency by performing fuel cut control for stopping fuel supply to an internal combustion engine when decelerating or when an engine is automatically stopped in an eco-run vehicle or a hybrid vehicle.

In an internal combustion engine equipped with an EGR device, if fuel cut control is performed while EGR gas is being introduced into the intake system by the EGR device, EGR gas remains in the intake system and the exhaust system during fuel cut control. The remaining EGR gas is sucked into the internal combustion engine when returning from the fuel cut control to the normal fuel injection control. In some cases, the residual EGR gas sucked into the internal combustion engine when returning to the normal control is discharged outside the vehicle without being sufficiently purified by the exhaust purification catalyst. On the other hand, in a hybrid system including an internal combustion engine and an electric motor as a power source, a clutch between the electric motor and the internal combustion engine is engaged to perform motoring during deceleration, and the residual EGR gas is opened by fully opening the throttle valve. Patent Document 1 describes a technique for purifying residual EGR gas by sending a gas to an exhaust purification catalyst.
JP 2002-256919 A JP-A-6-257518

  In an internal combustion engine equipped with an EGR device, if fuel cut control is performed while EGR gas is being introduced into the intake system by the EGR device, EGR gas remains in the intake system during the fuel cut control. The EGR gas is sucked into the cylinder when returning from the fuel cut control. If the amount of EGR gas at this time is excessively large, combustion instability such as misfire may occur when the internal combustion engine is started when returning from the fuel cut control.

  The present invention has been made in view of such problems, and provides a technique for stabilizing combustion at the time of return from fuel cut control to normal fuel injection control in an internal combustion engine equipped with an EGR device. It is intended.

In order to achieve the above object, an EGR control device for an internal combustion engine of the present invention provides:
An EGR device that causes a part of exhaust gas from the internal combustion engine to flow into the intake system of the internal combustion engine as EGR gas;
Fuel cut control means for performing fuel cut control for stopping fuel injection in the internal combustion engine when a predetermined fuel cut condition is satisfied;
Road condition acquisition means for acquiring the road condition on which the vehicle is traveling;
Based on the road condition acquired by the road condition acquisition means, a prediction means for predicting the timing at which the fuel cut condition is satisfied after the present time;
Control means for performing a process of reducing the amount of EGR gas present in the intake system of the internal combustion engine at a time point a predetermined time before the timing at which the fuel cut condition predicted by the prediction means is satisfied;
It is characterized by providing.

  Here, the “road condition in which the vehicle travels” may include not only information related to the shape of the road but also information related to the environment around the road, information related to the traffic condition, and the like.

  In addition, the “prediction unit” predicts the timing at which the fuel cut condition is satisfied after the present based on the above information acquired by the road condition acquisition unit. For example, when traveling on a road that is currently traveling in the current driving state, a prediction is made that a road situation that is likely to be decelerated such as a curve or a downhill appears after a certain period of time. Thereby, the timing at which the deceleration operation is performed, that is, the timing at which the fuel cut condition is satisfied can be predicted.

  The “control unit” performs a process of reducing the amount of EGR gas existing in the intake system (hereinafter referred to as an EGR gas reduction process) at a time point a predetermined time before the timing at which the fuel cut condition is predicted to be satisfied by the prediction unit. Do. Here, the “predetermined time” means that the EGR gas reduction process is started before the “predetermined time” from the timing at which the fuel cut control is expected to be performed, so that the internal combustion engine This time is determined so as to suppress the EGR rate of the gas in the intake system from becoming higher than the limit EGR rate. The “limit EGR rate” is determined based on the upper limit value of the EGR rate that can suppress the occurrence of combustion instability such as misfire.

  As described above, according to the present invention, the control for reducing the amount of EGR gas in the intake system of the internal combustion engine is performed before the fuel cut control is actually started. Therefore, the fuel cut control is actually started. At this point, the EGR gas amount in the intake system has already decreased to some extent. Accordingly, it is possible to suppress the EGR rate of the gas existing in the intake system from being higher than the limit EGR rate during execution of the fuel cut control. Thus, it is possible to suppress the occurrence of combustion instability such as misfire when the condition for returning from the fuel cut control to the normal fuel injection control is satisfied and the normal fuel injection control is started.

  In the present invention, the control means for performing the “EGR gas reduction process” described above can be configured as a means for reducing the amount of EGR gas flowing into the intake system.

Specifically, in the configuration of the present invention,
An adjusting means for adjusting the amount of EGR gas flowing into the intake system of the internal combustion engine by the EGR device;
The control means is configured such that at a time before the timing when the fuel cut condition predicted by the prediction means is satisfied, the amount of EGR gas flowing into the intake system of the internal combustion engine flows into the intake system at that time. The adjusting means may be controlled to be smaller than the amount of EGR gas that is present.

  Here, as the “adjusting means”, any means can be used as long as it has a function of adjusting the amount of EGR gas flowing into the intake system, such as an EGR valve. By controlling the adjusting means so that the amount of EGR gas flowing into the intake system is smaller than the amount of EGR gas flowing into the intake system at that time, the EGR gas reduction process can be realized.

  In the present invention, the control means for performing the above-mentioned “EGR gas reduction process” can be configured as means for discharging the EGR gas in the intake system to the outside of the intake system.

For example, in the configuration of the present invention,
A rotation speed increasing means for increasing the rotation speed of the internal combustion engine;
The control means increases the rotational speed of the internal combustion engine from the rotational speed at the time by the rotational speed increasing means at a time before a predetermined time from the timing when the fuel cut condition predicted by the prediction means is satisfied. Also good.

  In the above configuration, any means can be used as the “rotational speed increasing means” as long as it has a function of increasing the rotational speed of the internal combustion engine. For example, the rotation speed increasing means can be configured as means for lowering the shift of a vehicle on which the internal combustion engine is mounted. By increasing the rotational speed of the internal combustion engine with respect to the rotational speed at that time by means of the rotational speed increasing means, more gas in the intake system is sucked into the cylinder at an earlier stage. Processing can be realized.

  According to the present invention, in an internal combustion engine equipped with an EGR device, it is possible to stabilize combustion when returning from fuel cut control to normal fuel injection control.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its intake / exhaust system and control system in the present embodiment. In all of the following embodiments, the general configuration of the internal combustion engine and its intake / exhaust system and control system are common. The internal combustion engine 1 is a gasoline engine having a plurality of cylinders 18 (FIG. 1 shows a schematic view of one of the cylinders 18. The other cylinders have the same configuration). The piston 3 is slidably inserted into the cylinder 18, and the combustion chamber 2 is formed inside the cylinder 18 by the piston 3 and the inner wall of the cylinder 18.

  The combustion chamber 2 communicates with the intake passage 5 through the intake port 11, and communicates with the exhaust passage 6 through the exhaust port 8. The boundary between the intake port 11 and the combustion chamber 2 is opened and closed by an intake valve 12. Further, the boundary between the exhaust port 8 and the combustion chamber 2 is opened and closed by an exhaust valve 9.

  The intake port 11 is provided with a fuel injection valve 10 that injects and supplies fuel into the intake port 11. An ignition plug 15 for igniting the air-fuel mixture sucked into the combustion chamber 2 is provided at the upper part of the cylinder 18.

  The exhaust passage 6 includes an air-fuel ratio sensor 23 that detects an air-fuel ratio of exhaust gas in an active state, and nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), and particulate matter ( Exhaust gas purification device 7 for purifying PM) and the like is provided. A throttle valve 14 that can control the amount of intake air is provided in the intake passage 5. The intake passage 5 is provided with an air flow meter 13 and a surge tank 16 for detecting the amount of air introduced into the intake passage 5 (intake air amount).

  The intake passage 5 and the exhaust passage 6 are connected by an EGR passage 30. Part of the exhaust gas flowing through the exhaust passage 6 flows into the intake passage 5 via the EGR passage 30. Exhaust gas flowing into the intake system of the internal combustion engine 1 through the EGR passage 30 is referred to as “EGR gas”. In the EGR passage 30, an EGR cooler 31 and an EGR valve 32 are sequentially arranged from the upstream along the flow direction of the EGR gas flowing in the EGR passage 30 (indicated by an arrow in FIG. 1).

  The EGR cooler 31 is provided so as to surround the EGR passage 30 and cools the EGR gas flowing in the EGR passage 30. The EGR valve 32 is an electronic control valve (open / close valve) that is opened and closed steplessly, and can freely adjust the amount of EGR gas flowing through the EGR passage 30 and flowing into the intake passage 5. The EGR passage 30 and the EGR valve 32 in this embodiment correspond to the EGR device in the present invention.

  The internal combustion engine 1 includes an air-fuel ratio sensor 23 and an air flow meter 13 described above, a crank position sensor 21 that outputs an electric signal corresponding to a rotation angle of a crankshaft (not shown), and a depression amount (accelerator opening) of an accelerator pedal (not shown). And an accelerator position sensor 22 that outputs an electrical signal corresponding to the signal. Signals output from these various sensors are input to an ECU 20 that is a computer that controls the internal combustion engine 1. The ECU 20 controls the operation state of the internal combustion engine 1 by controlling the operation of various devices including the fuel injection valve 10, the EGR valve 32, the spark plug 15, and the throttle valve 14 based on signals input from these various sensors. Control.

  A vehicle (not shown) on which the internal combustion engine 1 is mounted is provided with a car navigation system (hereinafter referred to as “navigation”) 17. The navigation 17 includes maps, road shapes (eg, straight lines, curves, curvature of curves, slopes, etc.), road surrounding environments (railways, service areas, parking lots, etc.), traffic conditions (congestion information, construction information, weather information, etc.) The storage device stores various data such as, and / or an information acquisition system that downloads the various data from an online service or the like. The data that can be used by the navigation 17 may be any data as long as it includes information that can affect the traveling speed of the vehicle, and is not limited to the examples listed above. It is not necessary that all examples be available. The navigation 17 in this embodiment corresponds to the road condition acquisition means in the present invention. Examples of the “information that affects the traveling speed of the vehicle” include road shape information and road gradient information that the driver is most likely to decelerate, such as curves and downhills.

  By opening the EGR valve 32, EGR gas flows into the intake passage 5. By introducing the EGR gas into the intake system of the internal combustion engine 1 in this way, the cooling loss and the pump loss are reduced, so that the fuel efficiency can be improved. In addition, the amount of NOx contained in the exhaust can be reduced. However, if the EGR rate of intake air becomes excessively high, combustion may become unstable, and problems such as misfire and torque fluctuation may occur.

  The relationship between this EGR rate, combustion instability, and fuel consumption will be described with reference to FIG. In FIG. 2, the horizontal axis represents the EGR rate, and the vertical axis represents fuel consumption and torque fluctuation. As the EGR rate increases, the heat capacity of the intake air increases due to the inert gas in the EGR gas, and the combustion temperature decreases, thereby reducing the cooling loss. Further, when the amount of EGR gas increases, torque is not generated, the opening degree of the throttle valve 14 increases, and the pump loss decreases. As a result, in the region A, the EGR rate increases and the fuel consumption improves (fuel consumption decreases).

  As the EGR rate further increases, the ratio of inert gas increases and combustion deteriorates. Therefore, in region B, fuel consumption begins to deteriorate (increase in fuel consumption) and combustion becomes unstable and torque fluctuations suddenly increase. Worse. In this embodiment, the point where the excessive fuel instability does not occur and the fuel consumption is maximized (the boundary between the regions A and B) is set as the EGR limit value. Such a limit value is hereinafter referred to as a “limit EGR rate”.

In general, when the operating condition of the internal combustion engine 1 is low load and low rotation, since the amount of fresh air and the amount of fuel injection are small, combustion instability is likely to occur with the introduction of EGR gas. On the other hand, when the operating condition of the internal combustion engine 1 is high load and high rotation, stable combustion is performed, so that even if a large amount of EGR gas is introduced, combustion instability is unlikely to occur. FIG. 3 shows the relationship between the EGR rate of intake air and torque fluctuation in each case where the operating condition of the internal combustion engine 1 is low load and low rotation and high load and high rotation. For example, when the operating condition of the internal combustion engine 1 is a high load and high rotation speed, such as the EGR rate R _{EGR in} FIG. In this case, a large torque fluctuation may occur.

  Thus, in view of the fact that the upper limit (limit EGR rate) of the intake EGR rate at which combustion does not become unstable varies depending on the operating conditions of the internal combustion engine 1, in this embodiment, the operating conditions of the internal combustion engine 1 are high. The EGR control is performed so that the EGR rate of the intake air increases as the load becomes higher. FIG. 4 shows a map of the EGR rate determined for each operating condition of the internal combustion engine 1 (in the example of FIG. 4, the rotation speed and the load). As shown in FIG. 4, the EGR rate is increased as the rotational speed and / or load of the internal combustion engine 1 is increased. In addition, the introduction of EGR gas is stopped in a predetermined low-load low-rotation region indicated by diagonal lines in FIG.

  In the present embodiment, fuel cut control for stopping fuel injection by the fuel injection valve 10 is performed under predetermined operating conditions of the internal combustion engine 1. Examples of the predetermined operating condition include deceleration time. This predetermined operating condition is referred to as “fuel cut condition” in this embodiment. By performing fuel cut control when the fuel cut condition is satisfied, unnecessary fuel consumption can be suppressed and fuel consumption can be improved. During the fuel cut control, the EGR valve 32 is closed, and the introduction of EGR gas to the intake system is also stopped. In this embodiment, the ECU 20 that executes fuel cut control for stopping fuel injection by the fuel injection valve 10 when the fuel cut condition is satisfied corresponds to the fuel cut control means in the present invention.

  Here, when the fuel cut control is started when the internal combustion engine 1 is operated under the operation condition in which the EGR gas is introduced into the intake system, the EGR passage 30 and the EGR on the downstream side of the EGR valve 32 during the fuel cut control. EGR gas remains in the intake system region including the intake passage 5, the surge tank 16, and the intake port 11 on the downstream side of the connection portion of the passage 30.

  A part of the EGR gas remaining in the intake system region is sucked into the combustion chamber 2 and scavenged while the rotation of the internal combustion engine 1 decreases after the fuel cut control starts, but the fuel cut control starts. There may be a case where the air is not sufficiently scavenged from the intake system region due to the operating conditions of the internal combustion engine 1 immediately before. When the condition (return condition) for returning from the fuel cut control to the normal fuel injection control (normal control) is satisfied with the EGR gas remaining in the intake system region, first, the EGR gas remains in the intake system region. The EGR gas that is being discharged is sucked into the combustion chamber 2.

  In particular, when fuel cut control is started from an operating condition belonging to a high-load, high-rotation region where a large amount of EGR gas is introduced, a large amount of EGR gas remains in the intake system region when the return condition to normal control is satisfied. There is a possibility. In such a case, if the return to normal control is performed immediately when the return condition to normal control is satisfied, the residual gas having a high EGR rate in the intake system region is sucked into the combustion chamber 2 of the internal combustion engine 1. At the same time, fuel is supplied to the internal combustion engine 1 by the fuel injection valve 10. Therefore, there is a possibility that the EGR rate of the cylinder intake gas becomes excessively high beyond the limit EGR rate corresponding to the operating condition of the internal combustion engine 1 when the return condition is satisfied, and combustion instability such as misfire may occur.

A change in the EGR rate of the gas remaining in the intake system region during such fuel cut control will be described with reference to FIG. The horizontal axis of the graph of FIG. 5 represents time, and the vertical axis represents the limit EGR rate, the EGR rate of gas in the intake system region, the opening degree of the EGR valve 32, and the opening degree of the throttle valve 14. 5, when the normal control before the start of the fuel cut control (before time t ₀₎ is being performed, the EGR rate of the intake air is controlled to the target EGR ratio as defined in the map of FIG. The target EGR rate is set below the limit EGR rate. As a result, during normal control, combustion instability can be prevented from occurring while achieving fuel efficiency improvement effect and exhaust performance improvement effect.

When the fuel cut condition is satisfied at time t _0, the fuel cut control is started. At the same time, the EGR valve 32 is closed and the throttle valve 14 is closed. Thus, as indicated by the broken line A, the time t ₀ after the limit EGR rate is rapidly decreased. In addition, after time t ₀ , fuel injection is stopped by fuel cut control, but the internal combustion engine 1 continues to rotate due to inertia for a while, so that residual gas in the intake system region is sucked into the combustion chamber 2. It is scavenged. Thus, as indicated by the solid line B, EGR rate of the residual gas at time t ₀ after the intake system area also decreases.

However, as shown in FIG. 5, the decrease in the EGR rate of the residual gas is slower than the decrease in the limit EGR rate. After the fuel cut control is started, the EGR rate of the residual gas in the intake system region becomes the limit EGR rate. In some cases, it may exceed (in the example of FIG. 5, the period from time t _{A to} t _B ). When the duration of the fuel cut control is long (for example, when decelerating state continues for a long period of time, etc.), as the time t _B later in FIG. 5, EGR rate of the residual gas in the intake system area is sufficiently reduced In some cases, the EGR rate is below the limit.

  When the return condition to the normal control is established during the fuel cut control, the throttle valve 14 is opened again and the fuel supply to the internal combustion engine 1 is resumed. The remaining gas is sucked into the combustion chamber 2.

Accordingly, the fuel cut is performed at a time point (for example, time t _{2 in} FIG. 5) within a period (after time t _B in the example of FIG. 5) in which the EGR rate of the residual gas in the intake system region is decreased to the limit EGR rate or less. When the return condition from the control to the normal control is satisfied and the normal fuel injection control is started, it is considered that appropriate combustion is performed.

On the other hand, the fuel cut control is changed to the normal control at a time (for example, time t _{1 in} FIG. 5) within a period (time t _{A to} t _B ) in which the EGR rate of the residual gas in the intake system region exceeds the limit EGR rate. When the return condition is satisfied and normal fuel injection control is started, a gas having an EGR rate that is excessively higher than the EGR rate at which the fuel can be stably combusted is sucked into the combustion chamber 2. Instability of combustion such as misfire may occur.

  On the other hand, the target EGR rate predetermined as a map as shown in FIG. 4 is set to the limit EGR rate so that the EGR rate of the residual gas in the intake system region after the start of the fuel cut control can maintain a value equal to or lower than the limit EGR rate. By setting the value sufficiently low, it is possible to take measures to suppress combustion instability when returning from fuel cut control to normal control.

FIG. 6 shows the relationship between the EGR rate of the gas in the intake system region after the start of the fuel cut control and the limit EGR rate when the target EGR rate is set based on such a concept. As shown by the solid line B2 in FIG. 6, the EGR rate of the gas in the intake system region exceeds the limit EGR rate during the fuel cut control even if the rate of decrease in the EGR rate of the gas in the intake system region after the start of the fuel cut control is slow. Thus, the target EGR rate R _TRG2 (<R _TRG1 ) during normal control can be set.

  However, setting the target EGR rate to such a low value means that the EGR rate considerably lower than the limit line in FIG. 2 is set as the target EGR rate. That is, there is a possibility that the fuel efficiency improvement effect and the exhaust performance improvement effect due to the implementation of EGR cannot be sufficiently obtained.

Therefore, in this embodiment, a value close to the limit EGR rate at which a fuel efficiency improvement effect and an exhaust performance improvement effect can be sufficiently obtained is set as the target EGR rate. Then, the navigation 17 acquires information on the shape and gradient of the road that is predicted to travel from now on, and predicts the timing at which the fuel cut condition may be established in the near future based on the acquired information.

  For example, since it is generally considered that the driver decelerates before a curve or on a downhill, the navigation 17 acquires information that a curve or a downhill exists at a position that is a certain distance away on the currently traveling road. In this case, the time required to reach the curve or downhill from the current position is calculated based on the current vehicle speed, for example. Thereby, it is possible to calculate the timing at which the deceleration operation is predicted, that is, the timing at which the fuel cut condition is predicted to be satisfied.

  And the control which sets the opening degree of an EGR valve to the opening degree of a close side rather than the EGR valve opening degree in the time at the time of fixed time before the timing estimated in this way is performed. Thereby, the EGR rate of the gas existing in the intake system region can be made lower than the target EGR rate before the timing when the fuel cut condition is actually satisfied. Therefore, when the fuel cut condition is actually satisfied, the EGR rate of the gas in the intake system region can be already sufficiently lowered.

  Here, “the state where the EGR rate is sufficiently lowered” means that the EGR rate in the intake system region is such that the EGR rate of the residual gas in the intake system region does not exceed the limit EGR rate during fuel cut control. It means a lowered state. Therefore, even when fuel injection is performed to immediately return the internal combustion engine 1 to the normal control when the return condition to the normal control is satisfied during the fuel cut control, it is possible to suppress the occurrence of combustion instability such as misfire.

  Furthermore, the EGR rate of the intake air becomes lower than the target EGR rate before the timing at which the fuel cut condition is predicted to be satisfied from the time before the predetermined period before the timing until the time when the fuel cut condition is actually satisfied. This period is limited to a certain period. Therefore, it is possible to suppress a reduction in fuel consumption improvement effect and exhaust performance improvement effect due to the implementation of EGR.

  In the present embodiment, the fuel cut condition establishment timing is calculated based on the information acquired by the navigation 17 and processing for changing the opening degree of the EGR valve to the closing side opening is performed at a certain time before the timing. The ECU 20 corresponds to the control means in the present invention. This process is hereinafter referred to as “EGR gas reduction process”.

FIG. 7 is a time chart showing an example of a temporal change in the limit EGR rate, the gas EGR rate in the intake system region, and the EGR valve opening when the control according to the present embodiment is performed. Based on the information acquired by the navigation 17 and the information on the driving state such as the current vehicle speed, the time required to reach the position where the fuel cut condition such as deceleration is predicted to be satisfied from the current time (time t _N ). Δt _P is calculated, and a fuel cut condition establishment prediction time t ₀ is calculated.

Based on this prediction result, at a time point (time t _P ) before the fuel cut condition establishment prediction time t _{0 for} a certain time Δt _C , the EGR gas reduction process (in this embodiment, the EGR valve opening is determined as the time point t _P). in is determined that should start target degree of opening _{D TRG} than [Delta] D _C only closing side of the opening _{D C (= D TRG -ΔD C} ) for controlling the process).

Then, at time _{t P,} EGR valve opening by being controlled to the opening degree _{D C,} the EGR rate of the intake air is changed to the target EGR rate _{R TRG} lower EGR rate _{R C} at that time.

As a result, the EGR rate of the gas in the intake system region is reduced to a “sufficiently low EGR rate” when the fuel cut condition is satisfied at time t ₀ and fuel cut control is actually started. Can be.

Therefore, as shown in FIG. 7, the EGR rate (solid line B ₃ ) of the residual gas in the intake system region during execution of the fuel cut control is suppressed from exceeding the limit EGR rate (broken line A). Therefore, even when the condition for returning from the fuel cut control to the normal control is satisfied, even if the control of the internal combustion engine 1 is immediately returned to the normal control, combustion instability such as misfire can be suppressed.

  Here, the “certain time” means that the EGR gas reduction processing is performed at a time before the timing at which fuel cut control is predicted to start (in this embodiment, the EGR valve opening is set to the closed side). Thus, during the execution of the fuel cut control, the time is determined so that the EGR rate of the residual gas in the intake system region can be suppressed from becoming higher than the limit EGR rate. It is conceivable that the optimum time as the “certain time” varies depending on the amount of change in opening when the EGR valve opening is closed on the EGR gas reduction processing.

  For example, when the opening change amount (close amount) is reduced, the time required from when the EGR gas reduction process is started until the EGR rate in the intake system region sufficiently decreases is relatively long. ”Is set to a relatively long time, and the EGR gas reduction process needs to be started from a time point substantially before the timing at which the fuel cut condition is predicted to be established. That is, the implementation period of the EGR gas reduction process becomes longer.

  However, in this case, even during the execution of the EGR gas reduction process, the degree to which the intake EGR rate is lower than the target EGR rate is relatively small, so that it is considered that there is little influence on the fuel efficiency improvement effect and the exhaust performance improvement effect.

  On the other hand, when increasing the opening degree change amount (closing amount) of the EGR valve in the EGR gas reduction process, the time required for the EGR rate in the intake system region to sufficiently decrease after the EGR gas reduction process is started is compared. Therefore, it is sufficient to set the “certain time” to a relatively short time and start the EGR gas reduction process from a time relatively close to the timing at which the fuel cut condition is predicted to be established. That is, the implementation period of the EGR gas reduction process can be shortened.

  However, in this case, since the EGR rate of the intake air is considerably lower than the target EGR rate during the EGR gas reduction process, it is considered that the fuel efficiency improvement effect and the exhaust performance improvement effect are reduced to some extent. However, even if the effect due to EGR may be reduced, the period can be shortened, and the influence is considered to be sufficiently small as in the case described above.

In this embodiment, the optimal “certain time Δt _C ” (the EGR gas reduction process at the time when the fuel cut condition is predicted to be established) is optimal for fuel consumption, exhaust performance, drivability, combustion stabilization effect, and the like through experiments and simulations. The preceding time at the start time) and the “EGR valve closing amount ΔD _C ” (opening reduction correction amount with respect to the target EGR valve opening at the start of the EGR gas reduction process) are determined and used.

  FIG. 8 is a flowchart showing a routine for executing the control of the present embodiment described above. This routine is repeatedly executed at predetermined intervals during operation of the internal combustion engine 1.

In step S <b> 101, the ECU 20 determines, based on information acquired by the navigation 17, whether or not there is a place where it is predicted that the fuel cut condition will be satisfied after the present. If an affirmative determination is made in step S101, the ECU 20 proceeds to step S102. If a negative determination is made in step S101, the ECU 20 once ends the execution of this routine.

In step S102, ECU 20 determines the start time _{t P} of the EGR gas reduction process. Specifically, based on information about the operating condition of the road information and the current vehicle speed acquired by the navigation 17 calculates the time t ₀ when the fuel cut condition is expected to be established, from the time t ₀ the time _t P _{= t} 0 _{-Δt C} for a certain time before Delta] t _C a start time of the EGR gas reduction process.

In step S103, ECU 20 determines whether it is EGR gas reduction processing start time _{t P} calculated in step S102. If an affirmative determination is made in step S103, the ECU 20 proceeds to step S104. The ECU 20 repeats step S103 until an affirmative determination is made.

In step S104, the ECU 20 executes an EGR gas reduction process. More specifically, for controlling the EGR valve opening degree to the target EGR valve opening amount and close _{D TRG} [Delta] D _C closing side of the opening _{D C.}

In step S105, ECU 20 determines whether it is a fuel cut condition is satisfied predicted time _{t 0} calculated in step S102. If an affirmative determination is made in step S105, the ECU 20 proceeds to step S106. The ECU 20 repeats step S105 until an affirmative determination is made.

  In step S106, the ECU 20 determines whether or not a fuel cut condition is satisfied. If an affirmative determination is made in step S106, the ECU 20 proceeds to step S107. If a negative determination is made in step S106, the ECU 20 proceeds to step S108.

  In step S107, the ECU 20 starts fuel cut control. Specifically, the fuel injection is stopped and the throttle valve 14 and the EGR valve 32 are closed.

  In step S108, the ECU 20 determines that the vehicle has not traveled as predicted in step S101, and stops the EGR gas reduction process. That is, the EGR valve opening is returned to the normal target EGR valve opening. Also, normal control is performed for fuel injection.

In the above embodiment describes the control for changing the opening degree D _C fixed value [Delta] D _C only the closing side of the EGR valve opening relative to the target EGR valve opening at the start time t _P of the EGR gas reduction treatment , or continuously changing the opening degree of the EGR valve opening period from the time t _P at time t _0, may or stepwise changed the opening through the two-step or more steps. Further, in the case where actually the fuel cut-off condition even if the original time t ₀ when the fuel cut condition is predicted to be taken is not satisfied, fuel cut condition is satisfied prediction time t ₀ after a period of time the fuel cut conditions met After confirming the presence or absence, the return to the normal EGR valve opening degree control in step S108 may be performed. This “predetermined period” is determined by investigating in advance the degree of error that occurs regarding the prediction of the time when the fuel cut condition is established, or by factors that affect the time calculation error (such as road information and driving conditions that can be acquired from the navigation 17). ) And can be determined each time. Further, after performing EGR gas reduction processing (step S104), and without the whether it is a fuel cut condition is satisfied prediction time _{t 0} determined (step S105), determination of the presence or absence of incorporation fuel cut-off condition (step S106 ) And fuel cut control (step S107) may be performed based on the determination result.

  Next, a second embodiment of the present invention will be described. The difference between the present embodiment and the first embodiment is that, as an EGR gas reduction process, downshifting is performed instead of control for closing the EGR valve opening. Except for this point, the second embodiment is the same as the first embodiment, and a detailed description thereof will be omitted.

FIG. 9 is a diagram showing the relationship between the rotation speed and the vehicle speed for each shift. If the vehicle speed is equal, the number of revolutions of the internal combustion engine 1 increases by shifting down. For example, in the driving state at point A in FIG. 9 (shift 5 speed, vehicle speed V, rotation speed N _A ), by shifting down by one step, the driving state at point B in FIG. 9 (shift 4 speed, vehicle speed V, rotation speed). Number N _B ). As a result, the rotational speed increases by ΔN (= N _B −N _A ). As the rotational speed increases, the gas in the intake system region is sucked into the combustion chamber 2 earlier and more, so that the gas in the intake system region can be scavenged early.

  Therefore, in this embodiment, the timing at which the future fuel cut condition is satisfied is predicted based on the information of the navigation 17, and the control is performed to shift down as the EGR gas reduction process at a time before the predicted timing. It was.

  As a result, since the gas existing in the intake system region can be efficiently scavenged before the timing at which the fuel cut condition is actually satisfied, the intake system region at the time when the fuel cut condition is actually satisfied. The amount of EGR gas existing inside can be kept sufficiently reduced.

  “EGR gas amount is sufficiently reduced” means that the EGR gas amount in the intake system region is reduced so that the EGR rate of the residual gas in the intake system region does not exceed the limit EGR rate during fuel cut control. It means the state that is. Therefore, even when fuel injection is performed to immediately return the internal combustion engine 1 to the normal control when the return condition to the normal control is satisfied during the fuel cut control, it is possible to suppress the occurrence of combustion instability such as misfire.

  Further, the intake EGR rate becomes lower than the target EGR rate because the period from the time before the predetermined period before the fuel cut condition is predicted to be satisfied to the time when the fuel cut condition is actually satisfied, that is, Limited to a certain period. Therefore, it is possible to suppress a reduction in fuel consumption improvement effect and exhaust performance improvement effect due to the implementation of EGR.

FIG. 10 shows an example of the time variation of the limit EGR rate, the EGR rate of the gas in the intake system region, the EGR valve opening, the shift position, and the rotational speed of the internal combustion engine 1 when the control according to the present embodiment is performed. It is the time chart which showed. Based on the information acquired by the navigation 17 and the information on the driving state such as the vehicle speed, the fuel cut condition such as deceleration may be satisfied from the current time (time t _N ) to the time Δt _{P in the} future (time t ₀ ). is expected.

Based on the prediction result, the fuel cut condition is satisfied prediction time _t predetermined time from ₀ Delta] t _C a previous point in time (time _{t P),} the EGR gas reduction processing (in this embodiment, S from the shift _{S n} at the time _{t P} It is determined that the process of shifting down one step to _n-1 ) should be started. Then, at time t _P, S by being shifted down to _n-1, the rotational speed of the rotating speed of the internal combustion engine 1 is changed rotational speed NTRG the higher rotational speed N _C at that time.

As a result, scavenging of the gas in the intake system region is promoted, so that the EGR rate of the gas in the intake system region starts to decrease to an EGR rate lower than the target EGR rate _RTRG at that time. Thus, the EGR gas amount of the gas in the intake system region is in a “sufficiently reduced” state when the fuel cut condition is satisfied at time t ₀ and fuel cut control is actually started. Can do.

Therefore, as shown in FIG. 10, the EGR rate (solid line B ₄ ) of the residual gas in the intake system region during execution of the fuel cut control is suppressed from exceeding the limit EGR rate (broken line A). Therefore, even when the condition for returning from the fuel cut control to the normal control is satisfied, even if the control of the internal combustion engine 1 is immediately returned to the normal control, combustion instability such as misfire can be suppressed.

  The “certain time” in the present embodiment performs EGR gas reduction processing (in this embodiment, downshifting) at a time before the timing at which fuel cut control is predicted to be started. This time is determined so that the EGR rate of the residual gas in the intake system region can be prevented from becoming higher than the limit EGR rate during execution of the fuel cut control. It is conceivable that the optimum time as the “certain time” varies depending on the vehicle speed, the shift position, and the rotation speed when performing the downshift in the EGR gas reduction process.

For example, it is conceivable that as the vehicle speed at the time of downshifting increases, the range of increase in the rotational speed due to downshifting increases, so scavenging can be performed earlier. Accordingly, the “certain time” can be set to a short time. In this embodiment, the optimal “certain time Δt _C ” (the EGR gas reduction process at the time when the fuel cut condition is predicted to be established) is optimal for fuel consumption, exhaust performance, drivability, combustion stabilization effect, and the like through experiments and simulations. The preceding time at the start point) was determined and used. In addition, since there may be a feeling of deceleration due to the downshift, it is preferable that the downshift is one stage. However, as a control for achieving the effect of this embodiment of promoting the scavenging of the gas in the intake system region. Is not limited to that.

  FIG. 11 is a flowchart showing a routine for executing the control of the present embodiment described above. This routine is repeatedly executed at predetermined intervals during operation of the internal combustion engine 1.

  In step S201, the ECU 20 determines, based on information acquired by the navigation 17, whether or not there is a portion where the fuel cut condition is predicted to be satisfied after the present. If an affirmative determination is made in step S201, the ECU 20 proceeds to step S202. If a negative determination is made in step S201, the ECU 20 once ends the execution of this routine.

In step S202, ECU 20 determines the start time _{t P} of the EGR gas reduction process. Specifically, based on information about the operating condition of the road information and the current vehicle speed acquired by the navigation 17 calculates the time t ₀ when the fuel cut condition is expected to be established, from the time t ₀ the time _t P _{= t} 0 _{-Δt C} for a certain time before Delta] t _C a start time of the EGR gas reduction process.

In step S203, ECU 20 determines whether it is EGR gas reduction processing start time _{t P} calculated in step S202. If an affirmative determination is made in step S203, the ECU 20 proceeds to step S204. The ECU 20 repeats step S203 until an affirmative determination is made.

  In step S204, the ECU 20 executes an EGR gas reduction process. Specifically, it is shifted down by one stage.

In step S205, ECU 20 determines whether it is a fuel cut condition is satisfied predicted time _{t 0} calculated in step S202. If an affirmative determination is made in step S205, the ECU 20 proceeds to step S206. The ECU 20 repeats step S205 until an affirmative determination is made.

  In step S206, the ECU 20 determines whether or not a fuel cut condition is satisfied. If an affirmative determination is made in step S206, the ECU 20 proceeds to step S207. If a negative determination is made in step S206, the ECU 20 proceeds to step S208.

  In step S207, the ECU 20 starts fuel cut control. Specifically, the fuel injection is stopped and the throttle valve 14 and the EGR valve 32 are closed.

  In step S208, the ECU 20 determines that the vehicle has not traveled as predicted in step S201, and stops the EGR gas reduction process. That is, the shift is returned to the normal position. Also, normal control is performed for fuel injection.

In the above embodiment, when the fuel cut condition is not actually satisfied even at time t ₀ when the fuel cut condition is initially predicted to be satisfied, the fuel for a certain period after the fuel cut condition satisfaction predicted time t ₀ is reached. After confirming whether or not the cutting condition is satisfied, the process of returning to the normal shift position in step S208 may be performed. This “predetermined period” can be determined in the same manner as described in the first embodiment. Further, without determining whether or not becomes the fuel cut condition is satisfied predicted time t _0, after performing EGR gas reduction processing (step S204), whether the determination has become the fuel cut condition is satisfied predicted time t ₀ Without performing (Step S205), it may be determined whether or not the fuel cut condition is satisfied (Step S206), and the fuel cut control (Step S207) may be performed based on the determination result.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the above embodiment, the start timing of the EGR gas reduction process and the prediction of the fuel cut condition establishment timing are described in terms of time, but can be replaced with parameters such as the number of cycles and crank angle that can be mutually converted. . Also, the EGR gas reduction process of the first embodiment (EGR valve opening degree is closed) and the EGR gas reduction process (shift down) of the second embodiment can be performed in combination. By doing so, the residual EGR gas amount in the intake system region can be more reliably reduced.

It is a figure which shows schematic structure of the internal combustion engine in the Example, its intake system, and an exhaust system. It is a figure which shows the relationship between an EGR rate and a fuel consumption, and the relationship between an EGR rate and torque fluctuation. It is a figure for demonstrating the difference of the relationship between the EGR rate for every driving | running state of an internal combustion engine, and a torque fluctuation. It is a figure which shows the relationship between the driving | running condition of an internal combustion engine, and a target EGR rate. An example of the time variation of the limit EGR rate, the EGR rate of the gas in the intake system region, the EGR valve opening, and the throttle valve opening when fuel cut control is performed from the operating state in which EGR gas is introduced in the conventional system FIG. It is a figure for demonstrating the solution taken conventionally in order to suppress the combustion instability which may occur when returning from fuel cut control to normal fuel injection control. When the control of the first embodiment is performed, the time change of the limit EGR rate, the EGR rate of the gas in the intake system region, and the EGR valve opening when the fuel cut control is performed from the operation state where the EGR gas is introduced It is a figure which shows an example. 3 is a flowchart illustrating a routine for performing control according to the first embodiment. It is a figure which shows the relationship between the rotation speed of an internal combustion engine, and a vehicle speed for every shift position. In the case where the control of the second embodiment is performed, the limit EGR rate when the fuel cut control is performed from the operation state where the EGR gas is introduced, the EGR rate of the gas in the intake system region, the EGR valve opening degree, and the shift position It is a figure which shows an example of the time change of the rotation speed of an internal combustion engine. 6 is a flowchart illustrating a routine for performing control according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 3 Piston 4 Connecting rod 5 Intake passage 6 Exhaust passage 7 Exhaust purification device 8 Exhaust port 9 Exhaust valve 10 Fuel injection valve 11 Intake port 12 Intake valve 13 Air flow meter 14 Throttle valve 15 Spark plug 16 Surge tank 17 Car Navigation system 18 cylinder 20 ECU
21 Crank position sensor 22 Accelerator position sensor 23 Air-fuel ratio sensor 30 EGR passage 31 EGR cooler 32 EGR valve

Claims (5)

An EGR device that causes a part of exhaust gas from the internal combustion engine to flow into the intake system of the internal combustion engine as EGR gas;
Fuel cut control means for performing fuel cut control for stopping fuel injection in the internal combustion engine when a predetermined fuel cut condition is satisfied;
Road condition acquisition means for acquiring the road condition on which the vehicle is traveling;
Based on the road condition acquired by the road condition acquisition means, a prediction means for predicting the timing at which the fuel cut condition is satisfied after the present time;
Control means for performing a process of reducing the amount of EGR gas present in the intake system of the internal combustion engine at a time point a predetermined time before the timing at which the fuel cut condition predicted by the prediction means is satisfied;
An EGR control device for an internal combustion engine, comprising: In claim 1,
An adjusting means for adjusting the amount of EGR gas flowing into the intake system of the internal combustion engine by the EGR device;
The control means is configured such that at a time before the timing when the fuel cut condition predicted by the prediction means is satisfied, the amount of EGR gas flowing into the intake system of the internal combustion engine flows into the intake system at that time. An EGR control device for an internal combustion engine, wherein the adjusting means is controlled so as to be less than an amount of EGR gas. In claim 2,
The EGR device has an EGR passage that connects an exhaust passage and an intake passage of the internal combustion engine,
The adjusting means has an EGR valve provided in the EGR passage,
The control means has an opening degree of the EGR valve that is closer to a closing side than an opening degree of the EGR valve at the time point before a timing when the fuel cut condition predicted by the prediction means is satisfied. An EGR control device for an internal combustion engine, wherein the EGR valve is controlled to be In any one of Claim 1 to 3,
A rotation speed increasing means for increasing the rotation speed of the internal combustion engine;
The control means increases the rotational speed of the internal combustion engine from the rotational speed at the time point by the rotational speed increasing means at a time point a predetermined time before the timing at which the fuel cut condition predicted by the prediction means is satisfied. An EGR control device for an internal combustion engine. In claim 4,
The EGR control device for an internal combustion engine, wherein the rotation speed increasing means lowers a shift of a vehicle on which the internal combustion engine is mounted.

Images